The present invention relates to an apparatus for insertion into a manhole. More particularly, the present invention relates to an apparatus which is inserted into a manhole to prevent water leakage into the manhole.
Most cities and municipalities typically have two separate sewer systems, a sanitary sewer system and a storm water sewer system. The sanitary sewer system is designed to accept water that is discharged from homes and business including, but not limited to, water that is used in the toilet, cooking, bathing and washing clothes. All of the water that enters the sanitary sewer system is treated in a waste water treatment facility prior to being discharged into the environment.
The storm water sewer system is designed to accept large quantities of water from rainfall and melting snow. Typically, the water entering the storm water sewer is clean and not needing treatment. Therefore, the water transferred through the storm water sewer system is discharged directly into the environment without being treated in the waste water treatment facility.
Because all the water entering the sanitary sewer system is treated in a waste water treatment facility, municipalities and cities desire to keep the water intended to be transferred by the storm water sewer, which does not require treatment, from entering into the sanitary water sewer. Allowing clean storm water into the sanitary sewer system unnecessarily consumes capacity in the waste water treatment facility while increasing the costs of treating the water. When excessive storm water enters the waste water treatment plant, the waste water treatment plant may not have the capacity to treat the large amount of water causing untreated water, including raw sewage, to be discharged into the environment which can potentially cause an environmental disaster.
One of the major contributors of clean storm water entering the sanitary sewer is the design of most manhole structures which provide access to the sanitary sewer. The manhole box, typically a junction box, is positioned below ground level and has a through hole in the upper surface. A series of concrete rings called risers are positioned about the through hole on an upper surface of the manhole box. The risers bring the manhole structure up to approximately ground level while providing access to the manhole. A manhole cover frame is positioned on the upper surface of the upper riser such that the upper surface of the frame is at ground level. The manhole cover fits within the frame.
After the manhole box, the series of risers, the frame, and the cover are placed in the selected positions, the hole is backfilled to secure the structure in position. Water from rain and melting snow runoff can seep through the ground and enter the sanitary sewer system through seams between the manhole box and the first riser, between the seams between the risers, between the top riser and the frame and also between the frame and the manhole cover.
Besides having to treat clean runoff water in the waste water treatment plant, seepage of water also causes soil erosion around the manhole structure. As water enters into the sanitary sewer system through the manhole structure, the water also carries the surrounding soil into the manhole box. As the soil is eroded from around the manhole structure, a cavity is formed which over time will cause the soil above the cavity to collapse. When the soil collapses around the manhole cover, the surface needs to be filled in which adds additional repair expenses to the city or municipality.